Patent Document 1 discloses a crank angle detector for detecting a rotational angle of a crankshaft of an internal combustion engine, i.e., a crank angle. The crank angle detector includes: a toothed rotor, i.e., a signal rotor, which is attached to a crankshaft and is made of a magnetic material; and a magnet pickup coil. Along a circumference of the signal rotor, a plurality of tooth portions are arranged with uniform angular spacing. Also, at one portion of the circumference of the signal rotor, a tooth missing portion formed removing tooth portions. The tooth missing portion is used for detecting a reference position of the crank angle.
Generally, fuel injection timing (injection start timing and injection end timing) is first set as crank angles. Subsequently, based on the crank angle, a tooth portion serving as a reference (a reference tooth portion) is set. Also, a standby period until a point in time at which the fuel injection is started or ended after a detection signal corresponding to the reference tooth portion is detected is determined. When fuel injection control is executed, the reference tooth portion is detected by the magnet pickup coil. Thereafter, at a point in time at which a lapse of the standby period is determined through measurement by a timer, the fuel injection is started or ended.
The above-described standby period changes according to a rotational speed of the crankshaft. More specifically, from a duration between two detection signals respectively corresponding to any two adjacent tooth portions before the reference tooth portion, the rotational speed of the crankshaft is obtained. The obtained rotational speed is regarded as the present rotational speed of the crankshaft. In this way, the standby period in which the reference tooth portion is used as a point of origin is determined. When the duration between the detection signals corresponding to any two adjacent tooth portions is short, the obtained rotational speed of the crankshaft is fast, and thus, the standby period in which the reference tooth portion is used as the point of origin is also short.
In an 8-cylinder internal combustion engine as disclosed in Patent Document 1 and Patent Document 2, an interval between a previous fuel injection timing and the current fuel injection timing is equivalent to 90° in a crank angle. On the other hand, for example, in a case of a 4-cylinder internal combustion engine of which the number of cylinders is relatively small, the interval between the previous fuel injection timing and the current fuel injection timing corresponds to a crank angle of about 180°. Therefore, the engine of which the number of cylinders is greater has a shorter fuel injection interval. Recently, the number of internal combustion engines in which a pilot injection is performed before a main fuel injection or a post injection is performed after the main injection has been increasing. When the pilot injection or the post injection is performed in an engine of which the number of cylinders is relatively large, the fuel injection interval becomes very short. Thus, when the fuel injection timing is set according to the above-described method, the detection signal corresponding to the tooth missing portion may need to be used when the standby period serving a basis for calculating the injection timing is obtained.
However, the tooth missing portion is arranged over a zone in which a plurality of pieces of normal tooth portions can be located, and thus, in a detection zone of the tooth missing portions, the fuel injection timing needs to be set in a manner different from that of the detection zone of the normal tooth portions.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-303199
Patent Document 2: Japanese Laid-Open Patent Publication No. 2005-315107